Process of and apparatus for molding hollow rubber articles



J. A. LAW 2,098,395

PROCESS OF AND APPARATUS FOR MOLDING HOLLOW RUBBER ARTICLES Nov. 9,1937.

2 Sheets-Sheet'l Filed Aug. 16, 1934 James AHcm Law INVE T E.

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J. A, LAW

Nov. 9, 1937.

PROCESS OF AND APPARATUS FOR MOLDING HOLLOW RUBBER ARTICLES Filed Aug.16, 1934 2 Sheets-Sheet 2 11/1 A l 7 /6 /5 /2 /0 M /Z JBmcS Law \NVENTOB-Q L4ATT Patented Nov. 9, 1937 PROCESS OF AND ING HOLLOW V James Allan 7Law,

APPARATUS FOR MOLD- RUBBER ARTICLES Kensington, Victoria, AustraliaApplication August 16, 1934, Serial No. 740,128

a In Australia August 24, 1933 '4 Claims. (01. 18-42) This inventionrelates to improvements in the process of and means for molding hollowrubber balls described in United States of America Letters Patent No.1,877,673 dated 13th September, 1932. g

The object of this invention is to improve the said process andapparatus to ensure that spherical shells of uniform high quality foruse in the manufacture of tennis and like balls will be produced rapidlyand efliciently. This invention is characterized in that sulficientplastic rubber to form an article to be molded is placed on a removablecore, is trapped in the mold cavity and is then subjected to pressureuntil every part of such cavity is tightly packed with rubber, thusensuring the production of shells which conform exactly to the form ofthe cavity and each of which has walls of the predetermined thicknesswithout air bubbles or other defects.

This invention is further characterized in that apparatus for carryingthe said process into effect includes a, mold part having a wall orflange which engages a face on another mold part trapping the plasticrubber and holding it until it is subjected to suflicient pressure toensure that all parts of the mold cavity are-tightly packed,

. and in that spaced apart aperturesin the said wall are so located thatthe desired pressure is exerted on the rubber in the mold before excessrubber escapes through them.

But inorder that this invention may be more readily understood it willnow be described with reference to the accompanying drawings:-

In the drawings Figs. 1 to 4 are central vertical sections ofco-operating mold members illustrating the steps of manufactureaccording to this process.

Fig. 1 shows parts of a mold with a core located in the lower part andwith a quantity of plastic rubber on the top of the core.

Fig. 2 shows the mold members nearer to each other and with the rubberpartly distributed, the space between mold members being sealed by awall.

Fig. 3 shows the mold members closed together and with the coresurrounded by a formed shell.

Fig. 4 shows the mold again opened for removal of the core surrounded bythe formed shell.

Fig. 5 is a view of a multi-cavity mold partly in central verticalsection and partly in elevation.

Fig. 6 is a sectional plan on line 6-6 of Fig. 5.

Fig. 7 is a detail view of a mold guide.

Fig. 8 is a detail side view of a core support.

Fig. 9 is a plan of the core support shown in Fi 8. g 1 5 l0l I are moldmembers which are so supported that they may be moved toward, and fromeach other as desired. Thus either or both said 5 members may bemovable, and by way of example the drawings illustrate a mold in whichthe lower member in is movable relatively to a fixed upper member H.Mold member In contains any suitable number of hemispherical cavi- 10ties I2 each of which is arranged to co-operate with a hemi-sphericalcavity l2 in mold mem-- ber H, so that when the parts are closedtogether spherical cavities are formed.

There is a small clearance I 2 between the 15 adjacent faces of the moldmembers Ill-l I when the mold is closed, to permit rubber to flow and toallow surplus rubber to escape as hereinafter described. Such clearanceis for example, five one-thousandths of aninch in depth and theresultant fin on the molded articleis so thin-that 0 it is readilyremovable. V V

A peg 13 projects into each mold cavity l2 to engage a socket Iii in aremovable core I 4 in such manner that when the mold is closed, the

core is centralized within the spherical cavity. Each said peg hasgrooves l5 on its exterior leading to an air escape passage 15 throughthe peg l3. r a

To ensure accurate register, one mold mem- 3 her carries tapered guidepins I 6 which enter registering sockets It and said sockets are preferably provided with removable sleeves I 6*.

When each formed shell is to have a small hole in addition to the holeformed by peg l3, a projection ll enters each mold cavity l2sulficiently to engage a small hole M in the top of the core, thusensuring that the core will be centralized during molding.

Preferably each peg l3, pin l6 and projection I1 is fitted in a socketin a mold member, and each has a head which is retained by an adjacentstructure as Ill -I I so that the said members are firmly held inposition but are readily accessible and removable for repair or replace-45 0 arranged as closely together as convenient (see Fig. 6) and themold members are so supported that the co-operating mold cavities are inregister. In one case each mold part has a flange H3 in which are holesas It! to receive bolts or the 5 peripheral wall or flange ter withclearance l2 between adjacent mold.

faces but their position and area is such that rubber cannot escapebefore it is subjected to suflicient pressure to completely fill allmold cavities.

It will be understood that there may be a wall concentrically aroundeach cavity of one member of the mold, said wall being adapted to entera complementary groove which is concentric with the registering cavityin the other mold member but it is preferable to encompass a pluralityof cavities with a circular wall'as desc'ribed'and illustrated. V Incarrying the invention into operation the cavities of the lower moldmember II) are first painted with a suitable known solution to preventadhesion of rubber thereto. Cores [4 are then located and a wad 22 ofplastic rubber having a broad base and a pointed top is placed on eachcore. The controls are then operated to close the mold and as moldmembers approach each other the rubber is distributed (see Fig. 2) butbefore the flowing rubber can escape through the clearance it" it istrapped by the wall l9 engaging the face 20. Rubber will then be forcedinto each eavity'under pressure after which any surplus will escapethrough apertures 2| as before described. As the rubber enters the lowerpart of the mold cavities air escapes through grooves l5 and passage l5and between members It], H1 so that no obstruction is offered tocomplete filling of each cavity. The molded shells as S are thensubjected to heat until they are partly cured after which the mold partsare separated, the molded shells in the cores adhering to the upper moldpart so that a tool can be inserted in the core socket M to remove themfor further treatment in known manner. After the rubber shells eachcontaining a core have been removed from the mold, each shell isstripped from the core by forcing the latter through the hole formed inthe shell owing to the presence of peg l3. In my prior Patent 1,877,673,I have described the manner in which cores and the ball are separated,viz: Any suitable separating means may be employed: I find that a hookif engaged with the ball hole enlarges it sufficiently.

I claim:-

1. Mold devices for plastic rubber comprising two co-operating partshaving spaced apart cavities in registry, means to support a corecentrally in each cavity of one of the mold parts, a wall on one moldpart entirely surrounding the area of the mold and projecting beyond thesaid mold part to close the space between the said mold parts while theyare in spaced apart position and apertures in said wall, and means inthe other mold part to engage the cores to cause the adjacent faces ofthe mold parts to be spaced apart a short distance when the molds areclosed to their most adjacent position and when the mold parts are insuch position the apertures in the wall register with the space betweenthe said parts,

2. A mold, according to claim 1, in which one mold part is fixed and theother movable relatively thereto, the cores being arranged in thecavities in the fixed mold part and the apertured wall being a rim whichprojects from the movable mold part to encircle the fixed mold andslidably engage its peripheral face.

3. A mold, according toclaim 1, in which the spacing apart of theapertures causes the plastic rubber to be subjected tosufiicientpressure to force it into all parts of the mold cavities before theexcess rubber escapes through the said apertures.

4. A mold for plastic rubber comprising upper and lower mold memberseach having a plurality of spaced apart hemispherical mold cavities inregistry, means to support a spherical core centrally of each cavity ofthe lower mold member, a rim carried by the upper mold member arrangedtoencircle the lower member and slidably engage its peripheral face,spaced apart apertures in said rim, and means in the upper mold cavitiesto engage the cores and to cause the adjacent faces of themold membersto be spaced apart a short distance when in their most adjacent positionand the aperturesin the rim to be so arranged that they register withthe said space between the mold members when they are in said adjacentposition.

JAMES ALLAN LAW.

